RFID is a near-field RF identification and data exchange technique. An RFID system commonly comprises an RFID tag and an RFID reader. The RFID tag communicates with the RFID reader by generating an RF signal via a built-in antenna to transmit information stored in the RFID tag to the RFID reader, and the RF signal corresponds to a predetermined frequency. Generally, the RFID tag serves as a price tag or an indication tag, but is not used together with other external circuits. That is, the RFID tag neither transmits a received data to external circuits, nor transmits a data received from external circuits to the RFID reader via an RF approach. In addition, in some special applications, the RFID tag communicates with other circuits by an additional micro-control unit (MCU). However, usage of the additional MCU may substantially increase complexity and cost of the RFID tag and external circuits, and additional power supply needs to be provided to the MCU. Therefore, a solution for reducing complexity of data writing or reading between the RFID tag and other circuits as well as effectively reducing product cost of the overall RFID system is desired.